Method for dissolving saturated polyester solution for decomposing saturated polyester and method for decomposition using the same

ABSTRACT

The present invention provides a dissolution method for saturated polyester capable of recycling saturated polyester used in fibers, a film, a bottle and others with ease and a low cost, a solution decomposing saturated polyester and a decomposition method using the solution.

TECHNICAL FIELD

The present invention relates to a dissolution method for saturatedpolyester, a solution decomposing saturated polyester and adecomposition method using the solution, and more particularly, to adissolution method dissolving or decomposing saturated polyester tothereby enable a monomer or a prepolymer of the saturated polyester tobe recovered and recycled, a solution decomposing saturated polyesterand a decomposition method using the solution.

BACKGROUND ART

Since saturated polyester represented by polyalkylene terephthalate isexcellent in characteristics such as strength, transparency, heatresistance and chemical resistance, it has been used in variousapplications such as fibers, a film, a bottle and others.

In recent years, however, a great problem has been arisen with respectto recycling of spent saturated polyester occurring in an increasingamount or of a disqualified product occurring in production process forsaturated polymer, along with an increase in use amount thereof from theviewpoint of the global environment. Recycling methods for saturatedpolyester currently adopted are classified into three methods in a broadsense, that is a material recycling method, a thermal recycling methodand a chemical recycling method.

As the material recycling method, there have been known a method meltingsaturated polyester to mix it with a virgin raw material to reuse themixture, a method using only a recovered product to produce a low gradeproduct and the like method. Since a recycled product obtained by meansof the material recycling method is low in strength, a necessity arisesfor a measure to mix a recovered product with a virgin raw material.Since mixing of another plastic into saturated polyester has a problemto greatly reduce strength of a recycled product or color it, anecessity arises for selecting only saturated polyester strictly priorto melting.

While the thermal recycling method reuses heat generated in burningrecovered saturated polyester instead of a fuel, saturated polyester isburned in the method; therefore, it is not recycling and a problemarises in an environmental aspect because of generation carbon dioxidein combustion.

The chemical recycling method converts an abandoned saturated polyesterproduct back to a raw material to again synthesize saturated polyesterfrom the raw material, which enables recycling a resource that is anessential object, and which facilitates solving of the problems such ascontamination, mixing-in of different resin, reduction in molecularweight in molding, thermal coloration; therefore it is considered to bethe best recycling method. Examples of the chemical recycling methodinclude: (1) a hydrolysis method in which saturated polyester isheat-treated together with a strong acid or alkali aqueous solution tothereby convert the saturated polyester to phthalic acid as adicarboxylic acid such as terephthalic acid or a salt thereof forrecovery, (2) a methanol decomposition method in which saturatedpolyester is heat treated together with methanol to convert itdicarboxylic acid dimethyl ester such as dimethyl terephthalate forrecovery and (3) a glycol decomposition method in which saturatedpolyester is heat treated together with a glycol such as ethylene glycolor propylene glycol and thereby depolymerized to recover prepolymers ofsaturated polyester. Examples thereof include: a method described inJP-A No. 11-302208 using sodium hydroxide as a catalyst, a methoddescribed in JP-A No. 11-322677 in which glycol decomposition isfollowed by methanol decomposition, a method described in JP-A No.2000-53802 or 2000-169623 regenerating polyethylene terephthalate, amethod described in JP-A No. 2000-191766 using a titanium compound or atin compound as a catalyst, a method described in JP-A No. 2000-198876in which plastics other than polyethylene terephthalate are separatedoff and a method described in JP-A No. 2000-302707 using iron oxide as acatalyst.

In a chemical recycling method for saturated polyester currentlyavailable, however, high temperature in the vicinity of 200° C. isnecessary in order to advance an ester exchange reaction, whichtherefore has led to a problem to be unpreferable in regard to energyconsumption. In a case where an ester exchange reaction is performedusing a low-molecular-weight alcohol, the reaction is often performedunder high pressure in order to prevent the alcohol to be evaporatedoff, having led to problem of a need for an expensive high pressurevessel.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a dissolution methodfor saturated polyester in which the saturated polyester can be recycledwith ease and cost efficiency using a solution that can dissolvesaturated polyester even at low temperature under ordinary pressure.

It is another object of the present invention to provide a solution thatcan selectively disconnect an ester bond of saturated polyester even atlow temperature under ordinary pressure to produce a stable compoundserving as a raw material of saturated polyester.

It is another object of the present invention to provide a decompositionmethod for saturated polyester in which the saturated polyester can berecycled with ease and cost efficiency using a solution that candecompose the saturated polyester.

That is, the present invention relates to a dissolution method forsaturated polyester in which the saturated polyester is dissolved usingan amide solvent.

A dissolution method of the present invention is especially effective ina case where saturated polyester is polyalkylene terephthalate. It ispreferable that an amide solvent is a liquid at room temperature and hasa boiling point of 180° C. or higher and the amide solvent is especiallyN-methylpyrrolidone. The dissolution of saturated polyester ispreferably performed under ordinary pressure, and a temperature of anamide solvent in dissolution of saturated polyester is preferably atemperature equal to or higher than a freezing point thereof and equalto or lower than a boiling point thereof and especially preferably inthe range of from 130 to 190° C.

The present invention relates to a solution for decomposing saturatedpolyester that contains an alkali and a monoalcohol as a solvent or thatcontains a salt of a phosphorus-containing acid and a monoalcohol as asolvent.

Saturated polyester decomposed by a solution of the present invention ispolyalkylene terephthalate especially with efficiency. A monoalcohol ispreferably a lower alcohol and especially preferably methanol.

In a case where a solution of the present invention contains an alkaliand a monoalcohol as a solvent as a feature, the solution preferablydoes not contain a solvent other than a monoalcohol. In a case where asolution of the present invention contains a salt of aphosphorus-containing acid and a monoalcohol as a solvent as a feature,the solution preferably further contains, as a solvent other than amonoalcohol, at least one kind selected from the group consisting of anamide solvent, a ketone solvent, an ether solvent, an ester solvent anda hydrocarbon solvent. A salt of a phosphorus-containing acid ispreferably in the form of a hydrate thereof, more preferably an alkalimetal salt of a phosphorus-containing acid and especially preferablypotassium phosphate.

The present invention relates to a decomposition method for saturatedpolyester in which the saturated polyester is decomposed using asolution containing an alkali and a monoalcohol or a salt of aphosphorus-containing acid and a monoalcohol.

A decomposition method of the present invention is especially effectivein a case where saturated polyester is a polyalkylene terephthalate. Thedecomposition of the present invention is preferably implemented underordinary pressure, and a temperature of a solution in the decompositionis preferably equal to or higher than a freezing point thereof and equalto or lower than a boiling point thereof and more preferably equal to orless than 150° C.

At least one kind of decomposition product of saturated polyesterobtained by a decomposition method of the present invention is adicarboxylic acid dialkyl ester or a diol and the decomposition productcan be obtained in one step chemical reaction.

The present application claims priority from Japanese patent applicationNos. 2001-351068 (filed on Nov. 16, 2001), 2001-351073 (filed on 16 Nov.2001), 2001-351076 (filed on 16 Nov. 2001), 2001-351081 (filed on 16Nov. 2001) and 2001-351082 (filed on 16 Nov. 2001), the disclosures ofwhich are incorporated by reference herein.

BEST MODE FOR CARRYING OUT THE INVENTION

Saturated polyester used in a dissolution method, a solution and adecomposition method of the present invention is a polymer obtained bypolymerization of a dicarboxylic acid with a diol or a dicarboxylic acidester with a diol.

Examples of dicarboxylic acids include terephthalic acid, phthalicanhydride, isophthalic acid, adipic acid, naphthalenedicarboxylic acid,chlorendic anhydride, tetrabromophthalic anhydride, tetrahydrophthalicanhydride, tetrachlorophthalic anhydride, succinic acid, glutaric acid,trimellitic anhydride, cyclopentadiene-maleic anhydride adduct andothers.

Examples of dicarboxylic acid esters include dialkyl esters of adicarboxylic acid described above, such as dimethyl ester thereof,diethyl ester thereof, dipropyl ester thereof and dibutyl ester thereof.

Examples of diols include ethylene glycol, 1,4-butanediol,1,4-cyclohexanedimethanol, propylene glycol, diethylene glycol,neopentyl glycol, dipropylene glycol, dibromoneopentyl glycol,tripropylene glycol, triethylene glycol, polyalkylene glycol,cyclohexanedimethanol, trimethyl pentanediol,dihydroxydicyclopentanediol, bisphenol A, tetrabromobisphenol A,dialkoxybisphenol A, dialkoxytetrabromobisphenol A, hydroquinone,resorcinol, catechol; polycyclic bifunctional phenols such as bisphenolA, bisphenol F, biphenol, dihydroxydiphenyl ether anddihydroxydiphenylsilfone, and halogenides, alkyl group substitutedcompounds and isomers thereof.

Saturated polyester of the present invention may be obtained bycombining several kinds selected from the group consisting of thedicarboxylic acids, the dicarboxylic acid esters and the diols, and mayalso be obtained by the combination in the presence of a catalyst ifnecessary. Saturated polyester of the present invention may contain aninorganic filler such as glass fibers, glass powder, calcium carbonate,aluminum hydroxide, magnesium hydroxide, calcium silicate, mica, clay,titania, alumina, iron oxide, aluminum or the like.

Of saturated polyesters having constituents described above, alkyleneterephthalate such as polyethylene terephthalate and polybutyleneterephthalate are dissoluble or decomposable especially with goodefficiency by a dissolution or decomposition reaction of the presentinvention.

Then, description will be given of a dissolution method for saturatedpolyester as described above.

In a dissolution method of the present invention, saturated polyester isdissolved in an amide solvent. Examples of amide solvents that can beused in the dissolution include formamide, N-methylformamide,N,N-dimethylformamide, N,N-diethylformamide, acetamide,N-methylacetamide, N,N-dimethylacetamide, N,N,N′,N′-tetramethylurea,2-pyrrolidone, N-methyl-2-pyrrolidone, caprolactam, carbamic acid esterand the like, which are not specifically limited. The amide solvents maybe used either alone or in mixture of two or more kinds. Of the amidesolvents, preferable with respect to the purpose to efficiently performa dissolution reaction of the present invention is an amide solvent thatis a liquid at room temperature and has a boiling point of 180° C. orhigher and especially preferable is N-methylpyrrolidone. A use amount ofan amide solvent in the present invention is preferably in the range offrom 0.5 to 100 parts by weight and more preferably in the range of from1 to 10 parts by weight relative to 1 part by weight of saturatedpolyester.

Any of other solvents may be mixed with saturated polyester and an amidesolvent as far as it does not react with the saturated polyester and theamide solvent. Examples of such other solvents include a ketone solvent,an ether solvent, a hydrocarbon solvent, water and others.

Examples of ketone solvents include acetone, methyl ethyl ketone,2-pentanone, 3-pentanone, 2-hexanone, methyl isobutyl ketone,2-heptanone, 4-heptanone, diisobutyl ketone, cyclohexanone,methylcyclohexanone, acetophnone, phorone, isophorone and others.

Examples of ether solvents include dipropyl ether, diisopropyl ether,dibutyl ether, dihexyl ether, anisole, phenetole, dioxane,tetrahydrofuran, acetal, ethylene glycol dimethyl ether, ethylene glycoldiethyl ether, diethylene glycol dimethyl ether, diethylene glycoldiethyl ether and others.

Examples of hydrocarbon solvents include hexane, heptane, octane,nonane, decane, toluene, xylene, ethyl benzene, diethyl benzene, isomersthereof, halogenides thereof, and mixtures thereof.

In a dissolution method of the present invention, the other solvents canalso be used either alone or in mixture of a few kinds in arbitraryproportions.

In a case where saturated polyester is dissolved by means of adissolution method of the present invention, the saturated polyester ispreferably crushed into pieces with proper sizes so as to facilitate thesaturated polyester to be decomposed. Crushing is implemented using, forexample, an impact crusher, a shear crusher, a compression crusher, astamping mill, a ball mill, a rod mill and the others. While sizes ofcrushed pieces are not specifically limited, the sizes are preferably inthe range of from 0.1 cm³ to 1 m³ in consideration of a scale of anapparatus. If the sizes are less than 0.1 cm³, crushing takes a longertime, while if the sizes larger than 1 m³, a treatment time is longer,any of which cases conspicuously reduces a treatment efficiency.

A dissolution method for crushed saturated polyester pieces with anamide solvent is not specifically limited and exemplified are a methodin which the crushed saturated polyester pieces are immersed in an amidesolvent, a method in which an amide solvent is sprayed onto the crushedsaturated polyester and the like method.

A temperature at which saturated polyester is dissolved using an amidesolvent is not specifically limited as far as a solution assumes aliquid state and is arbitrarily determined so as to be equal to orhigher than a freezing point of a solution and equal to or lower than aboiling point thereof from the viewpoint of adjustability in desireddecomposition speed, treatability and others, wherein the temperature ispreferably in the range of from 130 to 190° C. A surrounding atmospherein the dissolution may be of an inert gas such as air, nitrogen, argon,carbon dioxide or the like, and a pressure thereof may be ordinarypressure or a pressure lower or higher than the ordinary pressure, amongwhich ordinary pressure is preferable in consideration of safety andsimplicity and convenience. In order to raise a dissolution speed, it iseffective to increase a temperature or to treat under pressure, or inaddition to agitate a solvent during immersion or to provide vibrationby ultrasonic wave.

In the dissolution, other plastics than saturated polyester may be mixedthereinto, such as polyethylene, polypopylene, polyvinyl chloride,polyamide, acrylic resin, polystyrene, ABS resin, polyurethane,polybutadiene, polyacetal, silicone resin, polymethylmethacrylate, urearesin, phenol resin, epoxy resin, polyimide and the like. The polymerscan be separated with ease after the dissolution since they are notcompatible with an amide solvent even if being melted by heat in thedissolution.

Metals, alloys thereof and oxides thereof may be mixed, such asaluminum, iron, zinc, tin, nickel, chromium, silicon and the like, andalloys and oxides thereof. Furthermore, inorganic materials may bemixed, such as glass, sand, alumina, porcelain, pottery and the like.Since the metals, metal oxides and inorganic materials are notdecomposed in an amide solvent, they can be easily separated after thetreatment.

A solvent is removed from a solution dissolving saturated polyesterobtained by the dissolution treatment and thereafter, the residual isheated to melt molded for possibility of recycling.

Then, description will be given of a solution decomposing saturatedpolyester described above and a decomposition method using the same.

A solution for decomposing saturated polyester of the present inventioncontains an alkali and a monoalcohol or a salt of aphosphorus-containing acid and a monoalcohol as indispensablecomponents.

Examples of alkalis, which are not specifically limited, used in asolution of the present invention include hydroxides, alcoholates andhydrides of alkali metals such as lithium, sodium, potassium, cesium andthe like. The compounds may be used either alone or in mixtures of a fewkinds. An impurity may be contained without causing a problem.

Examples of salts of phosphorus-containing acids, which are notspecifically limited, include salts of phosphoric acid, hypophosphoricacid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid,trimetaphosphoric acid, tetrametaphosphoric acid, pyrophosphorous acidand others with metals or cations of lithium, sodium, potassium,rubidium, cesium, beryllium, magnesium, calcium, strontium, barium,titanium, zirconium, vanadium, chromium, manganese, iron, cobalt,nickel, copper, zinc, aluminum, tin, ammonium and others. A saltdescribed above may be any of a first salt having one metal atom and twohydrogen atoms, a second salt having two metal atoms and one hydrogenatom and a third salt having three metals; may be any of an acidic salt,an alkaline salt and a neutral salt; and may be a hydrate. The compoundsmay be used either alone or in mixture of a few kinds. The compounds maycontain an impurity. Of the salts of phosphorus-containing acids, alkalimetal salts thereof are preferably for the purpose to perform adecomposition reaction of the present invention especially with goodefficiency, and especially preferable is potassium phosphate. Alsopreferable are hydrates of salts of phosphorus-containing acids.

Examples of monoalcohols as solvents used in a solution of the presentinvention include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol,2-butanol, iso-butanol, tert-butanol, 1-pentanol, 2-pentanol,3-pentanol, 2-methyl-1-butanol, iso-pentyl alcohol, tert-pentyl alcohol,3-methyl-2-butanol, neopentyl alcohol, 1-hexanol, 2-methyl-1-pentanol,4-methyl-2-pentanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol,3-heptanol, cyclohexanol, 1-methylcyclohexanol, 2-methylcyclohexanol,3-methylcyclohexanol, 4-methylcyclohexanol, ethylene glycol monomethylether, ethylene glycol monoethyl ether, ethylene glycol monopropylether, ethylene glycol monobutyl ether, diethylene glycol monomethylether, diethylene glycol monoethyl ether, diethylene glycol monopropylether, diethylene glycol monobutyl ether, triethylene glycol monomethylether, triethylene glycol monoethyl ether, benzyl alcohol,tert-butylbenzyl alcohol, methylbenzyl alcohol and chlorobenzyl alcohol,and isomers thereof. The monoalcohols can be used either alone or inmixtures of a few kinds in arbitrary proportions and can also be addedwith water. Of the monoalcohols, lower alcohols are preferably used forthe purpose to perform a decomposition reaction of the present inventionespecially with good efficiency and methanol is more preferable.

In a case where a solution is of an alkali and a monoalcohol as asolvent of a solution of the present invention, it is preferable not tocontain a solvent other than a monoalcohol, while in a case where asolution is of a salt of a phosphorus-containing acid and a monoalcoholas a solvent of a solution of the present invention, it is preferable tocontain additionally a solvent other than a monoalcohol, for example anamide solvent, a ketone solvent, an ether solvent, an ester solvent, ahydrocarbon solvent and others.

Examples of amide solvents include formamide, N-methylformamide,N,N-dimethylformamide, N,N-diethylformamide, acetamide,N-methylacetamide, N,N-dimethylacetamide, N,N,N′,N′-tetramethylurea,2-pyrrolidone, N-methyl-2-pyrrolidone, caprolactam, carbamic acid esterand the like.

Examples of ketone solvents include acetone, methyl ethyl ketone,2-pentanone, 3-pentanone, 2-hexanone, methyl isobutyl ketone,2-heptanone, 4-heptanone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, acetophnone, phorone, isophorone and others.

Examples of ether solvents include dipropyl ether, diisopropyl ether,dibutyl ether, dihexyl ether, anisole, phenetole, dioxane,tetrahydrofuran, acetal, ethylene glycol dimethyl ether, ethylene glycoldiethyl ether, diethylene glycol dimethyl ether, diethylene glycoldiethyl ether and others.

Examples of ester solvents include ethyl formate, propyl formate, butylformate, isobutyl formate, pentyl formate, methyl acetate, ethylacetate,propylacetate, isopropylacetate, butyl acetate, isobutyl acetate, pentylacetate, isopentyl acetate, methoxybutyl acetate, methylpentyl acetate,ethylbutyl acetate, ethylhexyl acetate, cyclohexyl acetate, benzylacetate, methyl propionate, ethyl propionate, butyl propionate,isopentyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate,butyl benzoate, γ-butyrolactone, ethylene glycol monoacetate, diethyleneglycol monoacetate, ethylene glycol diacetate, diethylene glycoldiacetate and others.

Examples of hydrocarbon solvents include hexane, heptane, octane,nonane, decane, toluene, xylene, ethyl benzene, diethyl benzene, isomersthereof, halogenides thereof, and mixtures thereof.

The solvents other than the monoalcohols can be used either alone or inmixtures of a few kinds in arbitrary proportions.

A mixing ratio in a solution containing an alkali and a monoalcohol ofthe present invention is such that an alkali can be adjusted at anyconcentration preferably in the range of from 0.1 to 90 wt % and morepreferably in the range of from 1 to 80 wt % relative to a monoalcohol,which is a solvent. A mixing ratio in a solution containing a salt of aphosphorus-containing acid and a monoalcohol of the present invention issuch that a salt of a phosphorus-containing acid can be adjusted at anyconcentration preferably in the range of from 0.1 to 90 wt % and morepreferably in the range of from 1 to 80 wt % relative to a monoalcohol,which is a solvent. In a case of a solution containing a salt of aphosphorus-containing acid and a solvent other than a monoalcohol inaddition to the monoalcohol, the salt of a phosphorus-containing acidcan be adjusted at any concentration in a similar range relative to atotal of the monoalcohol and the solvent other than the monoalcohol. Ina case of any of the solutions, if a concentration of an alkali or asalt of a phosphorus-containing acid is less than 0.1 wt %, adecomposition speed of saturated polyester is slow, while if exceeding90 wt %, it is difficult to prepare the solution. It is not alwaysnecessary for an alkali or a salt of a phosphorus-containing acid to bedissolved to the full and a solute is in equilibrium even in a saturatedsolution in which the alkali or the salt of a phosphorus-containing acidis not all dissolved, which situation is effective for making up fordiactivation of the alkali or the salt of aphosphorus-containing acid ifthe deactivation occurs. Furthermore, an additive agent such as asurfactant may be added to a solution of the present invention.

While no specific limitation is imposed on a temperature at which asolution of the present invention is prepared, it is preferably equal toor higher than a melting point and equal to or lower than a boilingtemperature. An surrounding atmosphere may be of air, an inert gas underany of ordinary pressure, a pressure lower or higher than the ordinarypressure.

In a case where saturated polyester is decomposed using a solution ofthe present invention, the saturated polyester is preferably crushedinto pieces with proper sizes to enable the saturated polyester, whichis an objective, to be decomposed. Crushing is implemented using, forexample, an impact crusher, a shear crusher, and a compression crusher,a stamping mill, a ball mill, a rod mill and the others. While sizes ofcrushed pieces are not specifically limited, the sizes are preferably inthe range of from 0.1 cm³ to 1 m³ in consideration of a scale of anapparatus. If the sizes are less than 0.1 cm³, crushing takes a longertime, while if the sizes are larger than 1 cm³, a treatment time islonger, any of which cases conspicuously reduces treatment efficiency.

A decomposition method for crushed saturated polyester pieces with asolution of the present invention is not specifically limited andexemplified are a method in which the crushed saturated polyester piecesare immersed in a solvent of the present invention, a method in which asolution of the present invention is sprayed onto the crushed saturatedpolyester and the like method.

A temperature at which saturated polyester is decomposed using asolution of the present invention is not specifically limited as far asthe solution assumes a liquid state and is arbitrarily determined so asto be equal to or higher than a freezing point of a solution and equalto or lower than a boiling point thereof from the viewpoint ofadjustability in desired decomposition speed, treatability and others,wherein the temperature is preferably equal to or lower than 150° C. andmore preferably equal to or lower than 100° C. A surrounding atmospherein the decomposition may be of air, an inert gas such as nitrogen,argon, carbon dioxide or the like, and a pressure thereof may beordinary pressure or a pressure lower or higher than the ordinarypressure, among which ordinary pressure is preferable in considerationof safety and simplicity and convenience. In order to raise adecomposition speed, it is effective to increase a temperature and totreat under pressure, and in addition to agitate a solvent duringimmersion and to provide vibration by ultrasonic waves.

In the decomposition, other plastics than saturated polyester may bemixed thereinto, such as polyethylene, polypopylene, polyvinyl chloride,polyamide, acrylic resin, polystyrene, ABS resin, polyurethane,polybutadiene, polyacetal, silicone resin, polymethyl methacrylate, urearesin, phenol resin, epoxy resin, polyimide and the like. The polymerscan be separated with ease after the treatment since they are notdecomposed in a solution containing an alkali and a monoalcohol or asolution containing a salt of a phosphorus-containing acid and amonoalcohol.

Metals, alloys thereof and oxides thereof may be mixed, such asaluminum, iron, zinc, tin, nickel, chromium, silicon and the like, andalloys and oxides thereof. Furthermore, inorganic materials may bemixed, such as glass, sand, alumina, porcelain, pottery and the like.Since the metals, metal oxides and inorganic materials are notdecomposed in a solution containing an alkali and a monoalcohol or asolution containing a salt of a phosphorus-containing acid and amonoalcohol, they can be easily separated after the treatment.

A decomposition product obtained by a decomposition treatment of thepresent invention contains at least a dicarboxylic acid dialkyl ester ora diol and no limitation is imposed on a product other than the ester orthe diol. In a case where a dicarboxylic acid dialkyl ester is addedwith an acid and thereby is altered to a dicarboxylic acid, and thedicarboxylic acid is precipitated from the solution when water is addedin excess thereinto. The dicarboxylic acid is washed with water anddried to thereby obtain a high purity dicarboxylic acid. Thedicarboxylic acid can be reused as a raw material for synthesis ofsaturated polyester.

A solution of the present invention used more than once is subjected tofiltration or the like to remove a decomposition product therefrom andsupplemented with an amount of shortage of a salt of aphosphorus-containing acid, an alkali, a monoalcohol or the like,thereby enabling the solution to be used repeatedly many times in orderto decompose saturated polyester.

In the present invention, a decomposition product as described abovecan, in such a way, be obtained by a one step chemical reaction.

While detailed description will be given of the present invention basedon examples, it should be understood that the present invention is notlimited to the examples.

(Dissolution Percentage of Saturated Polyester)

A plate of 0.35 mm thick made of polyethylene terephthalate(manufactured by Tsutsunaka Plastic Industry Co. LTD. with a trade nameof Sanroid Pet Ace EPG100) sold on the market as saturated polyester wascut to obtain test pieces each of 10 mm×30 mm in size. Various amidesolvents each in amount of 10.0 g were into respective glass test tubesof 20 ml in volume and a temperature of the solvent in the glass testtubes was kept at 60° C. using an oil bath. The test pieces were weighedand thereafter, immersed in the respective solvents, while aluminum capswere placed thereon in order to prevent the solvents from evaporatingtherefrom. The test pieces were taken out after a predetermined timeelapsed, washed with water, dried and again weighed, and then from achange between masses before and after the immersion of each test piece,a mass of dissolved saturated polyester was calculated as a dissolutionpercentage.

In Table 1, there are shown conditions for and dissolution percentagesof Examples 1 to 5 using various kinds of amide solvents and ComparativeExamples 1 to 8 using various solvents other than amide solvents.

TABLE 1 dissolution temperatures time percentages Solvents (° C.) (h)(%) Example 1 N,N-dimethyl 160 4.0 14.4 acetamide Example 2 N-methyl-160 4.0 71.3 pyrrolidone Example 3 N,N-dimethyl 140 4.0 5.8 formamideExample 4 N,N-dimethyl 140 4.0 3.6 acetamide Example 5 N-methyl- 140 4.028.1 pyrrolidone Comparative isophorone 160 4.0 −3.2 Example 1Comparative acetopheneone 160 4.0 −0.7 Example 2 Comparative diethylene160 4.0 0 Example 3 glycol monomethyl ether Comparative diethylene 1604.0 −0.7 Example 4 glycol diacetate Comparative diethylene glycol 1604.0 −1.3 Example 5 monobutyl ether acetate Comparative benzyl 160 4.0−3.7 Example 6 benzoate Comparative diethylene glycol 160 4.0 −0.7Example 7 dethyl ether Comparative triethylene glycol 160 4.0 −0.8Example 8 dimethyl ether

Polyethylene terephthalate in blocks was obtained by distillingsolutions of Examples 1 to 5 to thereby remove the solvent.

It was found that in cases where amide solvents were used as shown inExamples 1 to 5, polyethylene terephthalate is dissolved with ease. Itwas found that in contrast to this, in cases where solvents other thanamide solvents were used as shown in Comparative Examples 1 to 8,polyethylene terephthalate was not dissolved though being swollen.

(Decomposition Percentages of Saturated Polyester in Cases WhereDecomposition Solutions Containing Alkalis and Monoalcohols Were Used)

In Examples 6 to 15, polyethylene terephthalate (manufactured byTsutsunaka Plastic Industry Co. LTD with a trade name of Sanroid Pet AceEPG100) sold on the market as saturated polyester was cut to obtain testpieces each of 0.35 mm thick and 10 mm×30 mm in size; in Example 16,polyethylene butylene terephthalate was cut to obtain a test piece of0.35 mm thick and 10 mm×30 mm in size; and in Example 17, polyethylenenaphthalate was cut to obtain a test piece of 0.35 mm thick and 10 mm×30mm in size. A predetermined amount of each of solutions containingvarious kinds of alkalis and monoalcohols, which are solvents, was putinto a corresponding glass test tube of 20 ml in volume, the solutionsin the glass tubes were mildly stirred at room temperature andthereafter, a temperature in the solvent in the glass test tubes waskept at 60° C. using an oil bath. Masses of the test pieces were weighedand thereafter, the test rubes were immersed in the respective solvents,while aluminum caps were placed thereon in order to prevent the solventsfrom evaporating off therefrom. The test pieces were taken out after 4hours elapsed, washed with water, dried and masses of the test pieceswere again weighed, and then from a change between masses before andafter the immersion of each test piece, a mass of decomposed saturatedpolyester was calculated as a decomposition percentage.

In Table 2, there are shown conditions for and decomposition percentagesof Examples 6 to 17 and Comparative Examples 9 to 11. Note that, inExample 14, a procedure similar to that in Example 6 was adopted withthe exception that a cooling device was attached to a test tube and thetest piece was immersed in the solution at 64° C. under reflux and inExample 15, a procedure similar to that in Example 6 was adopted withthe exception that the test piece was immersed while the solution wasagitated with a magnetic stirrer.

TABLE 2 concentrations concentration temperature time decompositionAlkalis Solvents (eq/1000 g)^(note)) (wt %)^(note)) (° C.) (h)percentages Example 6 LiOH MeOH 1.00 2.3 60 4.0 12.9 Example 7 NaOH MeOH1.00 3.8 60 4.0 13.3 Example 8 KOH MeOH 1.00 5.3 60 4.0 11.1 Example 9LiOCH₃ MeOH 1.00 3.7 60 4.0 10.8 Example 10 NaOCH₃ MeOH 1.00 5.1 60 4.09.3 Example 11 KOCH₃ MeOH 1.00 6.5 60 4.0 9.8 Example 12 KOCH₃ DGMM 1.005.3 60 4.0 6.0 Example 13 LiOH MeOH 2.00 4.6 60 4.0 22.5 Example 14 LiOHMeOH 1.00 2.3 64 4.0 15.1 Example 15 LiOH MeOH 1.00 2.3 60 4.0 16.8Example 16 LiOH MeOH 1.00 2.3 60 4.0 13.8 Example 17 LiOH MeOH 1.00 2.360 4.0 10.3 Comparative — MeOH — — 60 4.0 0.2 Example 9 Comparative —DGMM — — 60 4.0 0.0 Example 10 Comparative KOH water 1.00 6.5 60 4.0 0.3Example 11 List of chemical formulae and abbreviated symbols LiOH:lithium hydroxide, NaOH: sodium hydroxide, KOH: potassium hydroxide,MeOH: methanol, LiOCH₃: lithium methoxide, NaOCH₃: sodium methoxide,KOCH₃: potassium methoxide, DGMM: diethylene glycol monomethyl ether^(note))Concentration (eq/1000 g): gram equivalents of a cation/1000 gof a solvent ^(note))Concentration (wt %): a concentration of a salt ofa phosphorus-containing acid relative to a monoalcohol

In Examples 6 to 11, 16 and 17, decomposition percentages were about 10%irrespective of relative low concentrations of various kinds of alkalis.By refluxing a solution with a cooling device mounted to a reactionapparatus as in Example 14 or by treating while being agitated as inExample 15, decomposition percentages can be raised. On the other hand,in Comparative Examples 9 to 11, no decomposition percentage of 1% orhigher were not be obtained.

Water in the same amount as the solutions obtained in Examples 6 to 17was added into the solutions and then a concentrated hydrochloric acidwas added into the solutions till the solutions becomes acidic, whenwhite crystals were precipitated. The white crystals were filtered out,washed with water, dried and measured with respect to infrared spectrathereof using Hitachi infrared spectrophotometer, Model No. 270-30 andmeasured with respect to nuclear magnetic resonance spectra of 1H and13C using a nuclear magnetic resonance apparatus BRUKER AC300P and, as aresult, were identified as terephthalic acid.

(Decomposition Percentages of Saturated Polyester in Cases WhereDecomposition Solutions Containing Salts of Phosphorus-containing Acidsand Monoalcohols Were Used)

A plate of 0.35 mm thick made of polyethylene terephthalate(manufactured by Tsutsunaka Plastic Industry Co. LTD. with a trade nameof Sanroid Pet Ace EPG100) sold on the market as saturated polyester wascut to obtain test pieces of 10 mm×30 mm in size. A predetermined amountof each of solutions containing various kinds of salts ofphosphorus-containing acids and monoalcohols, which are solvents, wasweighed and put into a corresponding glass test tube of 20 ml in volume,the solutions in the glass tubes were mildly stirred at roomtemperature. Then, a temperature in the solvent in the glass test tubeswas kept at a predetermined temperature using an oil bath. Masses of thetest pieces were weighted and thereafter, the test tubes were immersedinto the respective solutions and received a treatment, while aluminumcaps were placed thereon in order to prevent the solvents fromevaporating off therefrom. The test pieces were taken out afterpredetermined times elapsed, washed with water, dried and again weighed,and then from a change between masses before and after the immersion ofeach test piece, a proportion of dissolved saturated polyester wascalculated as a dissolution percentage.

In Table 3, there are shown conditions for and decomposition percentagesof Examples 18 to 65 and Comparative Examples 12 to 16.

TABLE 3 Salts of mono- solvent 1/ decomposition phosphorus- alcoholssolvent 2 concentrations concentrations temperature time percentagescontaining acids (solvent 1) solvent 2 (weight ratio) (eq/1000g)^(note)) (wt %)^(note)) (° C.) (h) (%) Example 18 Na₃PO₄ MeOH — — 1.005.2 60 4.0 1.8 Example 19 K₂HPO₄ MeOH — — 1.00 8.0 60 4.0 1.2 Example 20(NH₄)₃PO₄ MeOH — — 1.00 4.7 60 4.0 2.0 Example 21 K₄P₂O₇ MeOH — — 1.007.6 60 4.0 1.4 Example 22 K₃PO₄ MeOH — — 1.00 6.6 60 4.0 12.1 Example 23K₃PO₄ EtOH — — 1.00 6.6 60 4.0 2.7 Example 24 K₃PO₄ DGMM — — 1.00 6.6 604.0 3.0 Example 25 K₃PO₄ BZA — — 1.00 6.6 60 4.0 2.6 Example 26 K₃PO₄DGMM — — 1.00 6.6 160 4.0 36.4 Example 27 K₃PO₄ BZA — — 1.00 6.6 160 4.043.3 Example 28 K₃PO₄ MeOH — — 2.00 12.4 60 4.0 22.6 Example 29 K₃PO₄MeOH — — 5.00 26.1 60 4.0 42.6 Example 30 K₃PO₄ MeOH — — 10.00 41.4 604.0 65.9 Example 31 K₃PO₄ MeOH — — 20.00 58.6 60 4.0 82.9 Example 32K₃PO₄ MeOH — — 10.00 41.4 60 2.0 33.2 Example 33 K₃PO₄ MeOH — — 10.0041.4 60 6.0 56.8 Example 34 K₃PO₄ MeOH — — 10.00 41.4 60 10.0 86.7Example 35 K₃PO₄ MeOH — — 20.00 58.6 60 2.0 47.9 Example 36 K₃PO₄ MeOH —— 20.00 58.6 60 6.0 72.2 Example 37 K₃PO₄ MeOH — — 20.00 58.6 60 10.0100.0 Example 38 Na₃PO₄.12H₂O MeOH — — 1.00 11.2 60 4.0 2.2 Example 39K₃PO₄.nH₂O MeOH — — 1.00 8.3 60 4.0 6.1 Example 40 K₃PO₄.nH₂O EtOH — —1.00 8.3 60 4.0 2.9 Example 41 K₃PO₄.nH₂O DGMM — — 1.00 8.3 60 4.0 2.8Example 42 K₃PO₄.nH₂O BZA — — 1.00 8.3 60 4.0 3.2 Example 43 K₃PO₄.nH₂ODGMM — — 1.00 8.3 160 4.0 38.5 Example 44 K₃PO₄.nH₂O BZA — — 1.00 8.3160 4.0 41.4 Example 45 K₃PO₄.nH₂O MeOH — — 2.00 15.3 60 4.0 7.0 Example46 K₃PO₄.nH₂O MeOH — — 5.00 31.2 60 4.0 14.1 Example 47 K₃PO₄.nH₂O MeOH— — 10.00 47.6 60 4.0 18.1 Example 48 K₃PO₄.nH₂O MeOH — — 20.00 64.5 604.0 27.4 Example 49 K₃PO₄.nH₂O MeOH — — 1.00 47.6 60 10.0 32.1 Example50 K₃PO₄.nH₂O MeOH — — 10.00 47.6 60 10.0 73.2 Example 51 K₃PO₄.nH₂OMeOH — — 20.00 47.6 60 10.0 54.7 Example 52 K₃PO₄.nH₂O MeOH — — 1.0064.5 60 20.0 55.4 Example 53 K₃PO₄.nH₂O MeOH — — 10.00 64.5 60 20.0 91.1Example 54 K₃PO₄.nH₂O MeOH — — 20.00 64.5 60 20.0 100.0 Example 55 K₃PO₄MeOH water 1.0/1.0 1.00 8.3 60 4.0 2.7 Example 56 K₃PO₄ MeOHacetophenone 1.0/1.0 1.00 6.6 60 4.0 24.0 Example 57 K₃PO₄ MeOH methylethyl 1.0/1.0 1.00 6.6 60 4.0 28.3 ketone Example 58 K₃PO₄ MeOH acetone1.0/1.0 1.00 6.6 60 4.0 23.2 Example 59 K₃PO₄ MeOH N,N-dimethyl 1.0/1.01.00 6.6 60 4.0 22.7 formamide Example 60 K₃PO₄ MeOH N,N-dimethyl1.0/1.0 1.00 6.6 60 4.0 27.6 acetamide Example 61 K₃PO₄ MeOH N-methyl1.0/1.0 1.00 6.6 60 4.0 28.4 pyrrolidone Example 62 K₃PO₄ MeOH ethylene1.0/1.0 1.00 6.6 60 4.0 29.4 glycol diacetate Example 63 K₃PO₄ MeOHtoluene 1.0/1.0 1.00 6.6 60 4.0 28.7 Example 64 K₃PO₄.nH₂O MeOHN,N-dimethyl 1.0/1.0 1.00 8.3 60 4.0 27.6 acetamide Example 65 K₃PO₄MeOH N,N-dimethyl 1.0/1.0 10.00 41.4 60 4.0 77.2 acetamide. Comparative— MeOH — — — — 60 4.0 0.2 Example 12 Comparative — EtOH — — — — 60 4.00.3 Example 13 Comparative — DGMM — — — — 160 4.0 0.1 Example 14Comparative — BZA — — — — 160 4.0 0.2 Example 15 Comparative K₃PO₄ —acetophenone — — — 160 4.0 −0.7 Example 16 List of chemical formulae andabbreviated symbols Na₃PO₃: trisodium phosphate, Na₃PO₄.12H₂O: trisodiumphosphate dodecahydrate, K₃PO₄.nH₂O:tripotassium phosphate n-hydrate (atrade name, manufactured by KANTO KAGAKU with a content of tripotassiumphosphate in the range of 74 to 85%),K₂HPO₄: dipotassium phosphate,(NH₄)₃PO₄: triammonium phosphate, K₄P₂O₇: potassium pyrophosphate,K₃PO₄:tripotassium phosphate, MeOH: methanol, ^(note))Concentration (eq/1000g): gram equivalents of a cation/1000 g of a solvent^(note))Concentration (wt %): a concentration of a salt of aphosphorus-containing acid relative to a monoalcohol

As shown in Table 3, in Examples 18 to 65 using solutions containingvarious kinds of salts of a phosphorus-containing acids andmonoalcohols, decomposition percentages were all shown to be 1% or more.Among them, as shown in Example 37, conditions were found thatpolyethylene terephthalate is all decomposed at 60° C. for 10 h. Incases where solvents other than methanol were used together withmethanol as shown in Examples 56 to 65, decomposition percentages wereshown to be all larger than in a case where methanol alone was used by afactor in the range of from about 2 to 4. In contrast to the examples,in Comparative Examples 12 to 15, decomposition percentages were all 1%or less since the treatments were performed with solutions containingmonoalcohols only without containing salts of a phosphorus-containingacids and in Comparative Example 16, a decomposition percentage was 1%or less since a monoalcohol was not used as a solvent.

In Examples 18 to 37 and 46 to 54, water in amount ten times as much asthat of each solution was added to the solution after the correspondingdecomposition treatment, while in Examples 56 to 65, water in amount tentimes as much as that of each solution was added to the solution afterthe corresponding treatment, whereby white crystals were precipitated.Then, the solvents were removed by filtration, the salts ofphosphorus-containing acids were removed by washing the crystals withwater and thereafter, the crystals were dried to obtain white powder.The white powder was measured with respect to infrared spectra thereofusing Hitachi infrared spectrophotometer, Model No. 270-30 and measuredwith respect to nuclear magnetic resonance spectra of 1H and 13C using anuclear magnetic resonance apparatus BRUKER AC300P and as a result, wasidentified as dimethyl terephthalate because of coincidence with thespectra of dimethyl terephthalate. A purity thereof was 99%.

In each of Examples 18 to 37, a filtrate from the filtration wasdistilled at 100° C. or lower to remove the solvent and the residual wassubjected to filtration to separate a transparent liquid from the saltof a phosphorus-containing salt. As described above, the liquid wasmeasured with respect to infrared spectra thereof and measured withrespect to nuclear magnetic resonance spectra of 1H and 13C and as aresult, was identified as ethylene glycol because of coincidence withthe spectra of ethylene glycol.

In each of Examples 46 to 54, water in amount equal to a filtrate wasadded to the filtrate and a concentrated hydrochloric acid was added tothe diluted filtrate till being acidic, thereby precipitating whitecrystals. The diluted filtrate was filtered out to isolate the whitecrystals and the white crystals were washed with water, dried andmeasured with respect to infrared spectra thereof and nuclear magneticresonance spectra thereof, and as a result, were identified asterephthalic acid. A purity thereof was 98%. Note that a similarprocedure was applied to the filtrate of Example 22, in which case noproduction of terephthalic acid was observed.

In such a way, polyethylene terephthalate was able to be decomposed intodimethyl terephthalate and ethylene glycol, which are raw materials ofpolyethylene terephthalate, in one step reaction at a boiling point orlower of a solution under ordinary pressure. Furthermore, in an exampleusing a hydrate of a salt of a phosphorus-containing acid, terephthalicacid was able to be obtained.

Note that in all of the examples, use of a stirrer, a pressure vessel, acooling device and others promotes an efficiency of dispersion todefinitely reduce a treatment time. A treatment at a boiling point of asolvent or higher in a pressure vessel decreases a treatment time. Useof a cooling device enables a long time treatment at the boiling pointof a solution to be realized, which definitely reduce a treatment timeas well.

According to the present invention, since, as described above, saturatedpolyester can be dissolved or decomposed under ordinary pressure at alow temperature, saturated polyester can be recycled with more of easeat a lower cost as compared with those in a conventional technique.

A person skilled in the art shall understand that the above descriptionis preferred embodiments of the present invention and many ofalterations or modifications thereof can be implemented withoutdeparting from the spirit and scope of the present invention.

1. A solution for decomposing saturated polyester containing an alkaliand a monoalcohol as a solvent, and not containing a solvent other thanthe monoalcohol.
 2. The solution according to claim 1, wherein thesaturated polyester is polyalkylene terephthalate.
 3. The solutionaccording to claim 1, wherein the monoalcohol is a lower alcohol.
 4. Thesolution according to 1, wherein the monoalcohol is methanol.
 5. Asolution for decomposing saturated polyester containing a salt of aphosphorus-containing acid and a monoalcohol as a solvent.
 6. Thesolution according to claim 5, wherein the saturated polyester ispolyalkylene terephthalate.
 7. The solution according to claim 5,wherein the salt of a phosphorus-containing acid is in the form of ahydrate thereof.
 8. The solution according to claim 5, wherein the saltof a phosphorus-containing acid is an alkali metal salt of aphosphorus-containing acid.
 9. The solution according to claim 5,wherein the salt of a phosphorus-containing acid is potassium phosphateor potassium phosphate hydrate.
 10. The solution according to claim 5,wherein the monoalcohol is a lower alcohol.
 11. The solution accordingto claim 5, wherein the monoalcohol is methanol.
 12. The solutionaccording to claim 5, further containing, as a solvent other than amonoalcohol, at least one kind selected from the group consisting of anamide solvent, a ketone solvent, an ether solvent, an ester solvent anda hydrocarbon solvent.
 13. A decomposition method for saturatedpolyester, comprising decomposing the saturated polyester in thepresence of the solution according to claim
 5. 14. The decompositionmethod for saturated polyester according to claim 13, wherein thesaturated polyester is a polyalkylene terephthalate.
 15. Thedecomposition method for saturated polyester according to claim 13,wherein a temperature of the solution in the decomposition is equal toor higher than a freezing point thereof and equal to or lower than aboiling point thereof.
 16. The decomposition method for saturatedpolyester according to claim 13, wherein a temperature of the solutionin the decomposition is equal to or less than 150° C.
 17. Thedecomposition method for saturated polyester according to claim 13,wherein the decomposition is implemented under ordinary pressure. 18.The decomposition method for saturated polyester according to claim 13,wherein at least one kind of decomposition product of the saturatedpolyester is a dicarboxylic acid dialkyl ester.
 19. The decompositionmethod for saturated polyester according to claim 13, wherein at leastone kind of decomposition product of the saturated polyester is a diol.20. The decomposition method for saturated polyester according to claim13, wherein the decomposition product of the saturated polyester isobtained in one step chemical reaction.
 21. A decomposition method forsaturated polyester, comprising decomposing the saturated polyester inthe presence of the solution according to claim
 1. 22. The decompositionmethod for saturated polyester according to claim 21, wherein thesaturated polyester is a polyalkylene terephthalate.
 23. Thedecomposition method for saturated polyester according to claim 21,wherein a temperature of the solution in the decomposition is equal toor higher than a freezing point thereof and equal to or lower than aboiling point thereof.
 24. The decomposition method for saturatedpolyester according to claim 21, wherein a temperature of the solutionin the decomposition is equal to or less than 150° C.
 25. Thedecomposition method for saturated polyester according to claim 21,wherein the decomposition is implemented under ordinary pressure. 26.The decomposition method for saturated polyester according to claim 21,wherein at least one kind of decomposition product of the saturatedpolyester is a dicarboxylic acid dialkyl ester.
 27. The decompositionmethod for saturated polyester according to claim 21, wherein at leastone kind of decomposition product of the saturated polyester is a diol.28. The decomposition method for saturated polyester according to claim21, wherein the decomposition product of the saturated polyester isobtained in one step chemical reaction.
 29. The solution according toclaim 1, said solution further comprising said saturated polyester. 30.The solution according to claim 29, wherein said saturated polyester ispolyalkylene terephthalate.
 31. The solution according to claim 5, saidsolution further comprising said saturated polyester.
 32. The solutionaccording to claim 31, wherein said saturated polyester is polyalkyleneterephthalate.